Such prior art active devices have included a pressure transducer, a loudspeaker and an electronic control circuit adapted to generate, in response to pressure changes in the room, an electrical signal that serves to cancel the pressure change detected by the pressure transducer when it is reproduced through the loudspeaker. In the connection of this application, a loudspeaker means an entity constituted by one or more loudspeaker elements possibly operating over different frequency ranges.
Often when good sound reproduction is the aim attention is paid solely to the properties of the sound reproduction equipment. The listening space also has a great effect on the way the music sounds. In most cases, the listening room is the greatest factor influencing sound reproduction.
The acoustics of the listening room can be improved for instance by using different acoustic panels to line the walls and ceiling. Such passive methods are difficult to realize with frequencies below 200 Hz. To solve problems presented by low frequencies, the equipment described above has been provided, with which equipment room resonances can be attenuated or eliminated. This is based on the fact that the device can cancel low-frequency acoustic waves. Placed in a corner of a room, the device is able to attenuate standing waves present in said corner. Early reflections and reverberation found at higher frequencies, however, have a substantial effect on the character of the room as a listening space. A device of the kind described above in the prior art has no effect on the properties of the space in this respect. Typically, a normal room has too little early reflection and the reverberation is too sparse and has too short duration.